Color sensing device

ABSTRACT

A color sensing apparatus ( 10 ) includes an optical system ( 16 ) that produces a spatially uniform light beam ( 18 ).

BACKGROUND

Color sensing devices may include a light source that projects a lightbeam to a color sample to be measured and a sensor that detects thelight reflected by the sample to determine if a correct color wasprinted on the sample. However, if the sample is not accuratelypositioned the sensor may detect an inaccurate color reading because alight intensity of the light reflected by the sample may vary dependingon the sample's position. Accordingly, it may be desirable to provide acolor measurement device that reduces inaccurate color measurementreadings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of one example embodiment of a colorsensing device.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of one example embodiment of a colorsensing device 10. Device 10 may include a light source 12 that projectsa source light beam 14 to an optical element 16. Light source 12 may beany type of light source such as an incandescent light bulb, a lightemitting diode (LED) or the like, for example. Accordingly, source lightbeam 14 may be white light, or a particular range of light wavelengths,for example.

Optical element 16 receives source light beam 14 and produces an outputlight beam 18. Source light beam 14 is spatially scrambled as itpropagates to an object plane 20, i.e., an exit plane, of opticalelement 16. Spatially scrambled means adjusting the relative positionsof rays emitted from the light source 12 and repositioning them ontoother sections of a secondary image plane such as object plane 20, thusthe rays of output light beam 18 coming from the secondary source,object plane 20, are not correlated to the initial light source 12 thatcreated them. Stated another way, one definition of a spatially uniformlight beam may be that “each point of an exit face of a light tunnel hassome content of light rays from all or most points of an input lightsource distribution.” Thus optical element 16 may also be described as alight integrator 16 that produces a scrambled, rearranged, randomized,or integrated, output light beam 18.

Optical element 16 can alter the power distribution of light beam 14 atobject plane 20. Adjusting the power distribution at object plane 20 canoff set power distribution changes that occur when looking at the powerdistribution on a tilted media plane 38, such as defined by a sheet ofprint media 34 supported on a media support 26, which may be positionedat an acute angle 60 with respect to an axis 32 of output light beam 18.Because the image of object plane 20 is not parallel to media plane 38in device 10, without any correction as is supplied by device 10, thepower distribution will tend to have a non-spatially uniformdistribution near media plane 38. Accordingly, a tapered inlet surface16 a, on the front end of optical element 16 may adjust the powerdistribution to create the spatially uniform beam 18 only in the regionaround media plane 38. Thus, tapered inlet surface 16 a, in conjunctionwith optical element 16 may create the spatially uniform beam 18 in theregion of media plane 38.

Tapered inlet surface 16 a acts to re-apportion the spatial distributionof the light source 12 on object surface plane 20 of optical element 16.Thus the angled surface 16 a directs the light beam 14 by refractionwith an angular deviation that is set by the angle of the input light tothe angle of tapered surface 16 a. When source light beam 14 hasmultiple angles of light that comprise it, each light angle will refractdifferently. This allows a preferential redistribution of light beam 14as the multiple angles of light propagate down optical element 16. Theangle of tapered inlet surface 16 a is set by the length of element 16as well as the amount of re-apportioning that is needed to get thedesired power distributionon the media plane 38. Tapered inlet surface16 a may also have only a portion of its surface angled while the otherportion may be flat or define a surface normal to the beam axis 32 ofsource 12. This may allow some greater selectivity of where the light ofsource light beam 14 gets re-apportioned on object surface 20 of opticalelement 16.

Optical element 16 may be a hollow tube with a beam steering element infront of it such as a wedge that defines a tapered front surface 16 a,or a solid elongate member with a tapered inlet surface 16 a, forexample, manufactured of a material having an index of refractiongreater than an index of refraction of air, such as a solid elongatemember manufactured of glass. In embodiments wherein the axis 32 ofoutput light beam 18 and the axis 54 of color sensor 48 aresubstantially parallel, a tapered inlet surface 16 a on optical element16 may not be utilized.

A spatially uniform light beam is not the same as a collimated lightbeam, which may be defined as a light beam in which the nominal raydirections in the beam are parallel. Beam uniformity at a given plane isdecoupled from the angular extent of the beam. Thus, at any given pointin space a beam may have spatial uniformity, meaning that there isapproximately constant power as a function of position, but may be madeup of light rays at many different angles. The amount of beamcollimation is not a sufficient condition for defining beam spatialuniformity. Stated another way, a light beam having a spatially uniformdistribution of light intensity may include non-collimated light atdifferent angles that are overlaid on one another to define an even or aconstant intensity across the light beam exit, such as across an objectplane

Optical element 16 may define a cross sectional shape 22 (shown inperspective view as dash lines for ease of illustration) that may definethe shape of a light spot 24 output from the object plane 20 of opticalelement 16 and projected to a print media support 26. For example,optical element 16 may define a square, rectangular, trapezoidal, orcircular cross sectional shape 22, for example, and may therefore definea corresponding square, rectangular, trapezoidal, or circular crosssectional shape of light spot 24.

Optical element 16 may include a first field lens 28 secured to opticalplane 20, i.e., secured to the end 20, of optical element 16. In oneembodiment first field lens 28 may be glued to optical plane 20 ofoptical element 16. A second lens 30 may be positioned between firstfield lens 28 and print media support 26, along an output source lightbeam axis 32, that extends from optical element 16 to print mediasupport 26. First and second lenses 28 and 30, and any other lenses oroptical devices positioned along output light beam axis 32, may projectoutput light beam 18, projected from optical plane 20 of optical element16, to print media support 26 without allowing output light beamenvelope 18 to converge or diverge after passing through lens 30. Inother words, field lens 28 and lens 30 project a non-diverging andnon-converging output light beam 18 to print media support 26, withoutchanging the bounds of the projected output light beam 18 from the pathfrom lens 30 to the media plane 38. Thus by design of lenses 28 and 30and the optical element 16 incorporating tapered inlet surface 16 a, thebeam spatial uniformity and approximately constant power envelope ofbeam 18 can be achieved in the region near media plane 38. Tapered inletsurface 16 a of optical element 16 may define an angle 16 b of taperdependent upon angle 60 between axis 32 and media plane 38 of sheet ofprint media 34 so as to provide spatial uniformity of output light beam18 in the region of anticipated reflection region 58.

Print media support 26 may support thereon a sheet of print media 34.Device 10 may be utilized to determine whether a printed color region 36(shown in end view) printed on print media 34 is of a desired colorquality. In other words, device 10 may be used to sense the color ofprinted color region 36 to determine if a color printing device, whichmay be a component of device 10, is working satisfactorily. In oneexample, printed color region 36 may be a large area of printed red inkon a top surface 38 of print media 34.

Print media support 26 may include downwardly extending ribs 40 that mayallow portions of print media 34 to bend or cockle downwardly thereinsuch that top surface 38 of sheet of print media 34 may be positioned ata low position 42 (shown in dash lines) below a top surface 44 of printmedia support 26. In another embodiment, such as when measuring adifferent sheet of print media 34, the sheet of print media 34 may bendor cockle upwardly from print media support 26 such that top surface 38of sheet of print media 34 may be positioned at a high position 46(shown in dash lines) above top surface 44 of print media support 26.

During operation, output light beam 18 is projected to sheet of printmedia 34 and a portion of output light beam 18 is reflected therefrom asreflected light 52 along a reflected light axis 54. The portion ofoutput light beam 18 that is reflected as reflected light 52 may bedetermined by the color of printed color region 36 on sheet of printmedia 34. Accordingly, a color sensor 48, which may include or beconnected to a controller 56, may accurately determine the color ofprinted color region 36 by an analysis of reflected light 52, and inparticular, by an analysis of the light intensity of reflected light 52.

During color measurements, if the power per measured area (of light 52reflected from printed color region 36) changes as the sample is shiftedin position, there will be a perceived change in brightness of thesample even though the test sample did not change it reflectance. Inprior art devices, the measured light intensity of reflected light mayvary greatly depending on the position of a sheet of print media on itssupport. Such inaccurate light intensity measurements may be due to theuse of a non-spatially uniform output light beam, and/or due to the useof either a converging or a diverging output light beam. For example, ifa sheet of print media is cockled upwardly or downwardly a distance ofeven 0.25 millimeters (mm) from its support, wherein the support maydefine an anticipated position of the sheet of print media, then thelight intensity measured by a color sensor may be inaccurate, such thatthe true color printed on the sheet of print media is not accuratelydetermined by the color sensor. The present invention overcomes thesedisadvantages of the prior art by providing a spatially uniform outputlight beam 18 around the region of the anticipated reflection position58, and/or a non-converging or a non-diverging output light beam 18 tothe color region 36 to be measured. Use of a spatially uniform outputlight beam 18 in the region of the anticipated reflection position 58,and/or use of a non-converging or a non-diverging output light beam 18may allow slight positional inaccuracy of a sheet of print media 34 withrespect to an anticipated reflection position 58, without appreciablychanging the light intensity measurement as measured by a color sensor48.

Due to the spatially uniform, and/or non-converging and non-divergingnature of output light beam 18 in the region of the anticipatedreflection position 58 that is transmitted to sheet of print media 34 onprint media support 26, a color sensor 48 may detect or sense anaccurate color measurement of printed color region 36 on sheet of printmedia 34 even if sheet of print media 34 is not accurately positioned inan anticipated reflection position 58, i.e., even if sheet 26 is notpositioned on the plane of top surface 44 of print media support 26. Inother words, so long as sheet of print media 34 is positioned within arange of focus 50 of color sensor 48, an accurate measurement of thecolor of printed color region 36 may be determined by color sensor 48.Range of focus 50 of color sensor 48 may be determined by low position42 of print media 34 and high position 46 of print media 34 during aparticular color sensing operation. Accordingly, spatially uniform,and/or non-converging or non-diverging output light beam 18 in theregion of the anticipated reflection position 58 allows a sheet of printmedia 34 to be positioned anywhere within range of focus 50 and stillprovide an accurate color measurement by color sensor 48. In otherwords, device 10 enables color measurements to be made with a reducedsensitivity to height variations of a test sample when making colormeasurements. The illumination device 10 may be optimized for uniformityof the printed color region 36 as well as maintaining a relativelyconstant power into the printed color region 36 with vertical shifts ofthe sheet of print media 34 along axis 54.

Use of such a substantially height insensitive color measurement device10 may be particularly useful for measuring printed color regions 36 ona variety of print media 34, such as paper, card stock, mylar,cardboard, fabric, and the like, which may each define a unique heightof thickness.

Still referring to FIG. 1, device 10 may further include opticalelements, such as lenses 64 and 66, that are positioned along areflected light axis 54 of reflected light 52, wherein reflected lightaxis 54 may also be referred to as a sensor axis 54.

In the embodiment shown axis 54 of reflected light 52 may be positionedperpendicular to top surface 44 of print media support 26 and axis 32 ofoutput light beam 18 may be positioned at an angle 60 of approximatelyforty-five degrees with respect to top surface 44 of print media support26. Lenses 64 and 66 may be positioned and sized such that all reflectedlight 52 from printed color region 36 of sheet of print media 34 will betransmitted to color sensor 48 so long as top surface 38 of sheet ofprint media 34 is positioned within range of focus 50. In particular,when sheet of print media 34 is positioned on top surface 44 of printmedia support 26, reflected light axis 54 a is centered within andextends through lenses 64 and 66. When sheet of print media 34 ispositioned at high position 46, reflected light axis 54 b is positionedwithin and extends through lenses 64 and 66. When sheet of print media34 is positioned at low position 42, reflected light axis 54 c ispositioned within and extends through lenses 64 and 66. Accordingly, inall positions of sheet of print media 34 within range of focus 50, colorsensor 48 will receive substantially a single intensity measurement ofreflected light 52 along reflected light axis 54 such that an accuratecolor measurement of printed color region 36 may be determined withslight positional variations of the sample. Range of focus 50 may alsobe referred to as a reflection region and in one embodiment may define alength 62 of at least 2.5 mm, measured parallel to axis 54.

Other variations and modifications of the concepts described herein maybe utilized and fall within the scope of the claims below.

1. A color sensing apparatus (10), comprising: an optical system (16)that produces a spatially uniform light beam (18); and a color sensor(48) that senses reflected light (52) of a reflection of said spatiallyuniform light beam; wherein said optical system (16) is chosen from oneof a hollow light pipe and a solid elongate member manufactured of amaterial having an index of refraction greater than air; and whereinsaid optical system (16) includes a tapered inlet surface (16 a) thatdefines an acute angle with respect to an output light beam axis (32).2. A color sensing apparatus (10), comprising: an optical system (16)that produces a spatially uniform light beam (18); a color sensor (48)that senses reflected light (52) of a reflection of said spatiallyuniform light beam; a lens (28) positioned between said optical systemand a reflection region (58) of said spatially uniform light beam,wherein said optical system and said lens together produce saidspatially uniform light beam, and wherein said lens projects saidspatially uniform light beam to said reflection region while preventingsaid spatially uniform light beam from converging and from divergingduring said projection; and a second lens (30), one of said lens (28)and said second lens (30) secured to an end (20) of said optical systemand a. remaining one of said lens and said second lens spaced from saidoptical system and positioned between said optical element and saidreflection region.
 3. A method of making a color sensor (10),comprising: positioning a light integrator (16) adjacent a reflectionregion (58) such that light projected from said light integrator(18)will be reflected from said reflection region along a sensor axis (54);positioning a color sensor (48) along said sensor axis so as to receivelight reflected from said reflection region; and securing a field lens(28) to an end (20) of said light integrator (16), said field lenstransmitting said light projected from said light integrator to saidreflection region, wherein said transmitting comprises transmittingnon-diverging and non-converging light to said reflection region.
 4. Amethod of making a color sensor (10), comprising: positioning a lightintegrator (16) adjacent a. reflection region (58) such that lightprojected from said light integrator(18) has an approximately constantpower as a function of position and will he reflected from saidreflection region along a sensor axis (54); positioning a color sensor(48) along said sensor axis so as to receive light reflected from saidreflection region; and securing a field lens (28) to an end (20) of saidlight integrator (16), said field lens transmitting said light projectedfrom said light integrator to said reflection region, wherein saidtransmitting comprises transmitting non-diverging and non-converginglight to said reflection region.